1. Field of the Invention
The invention relates generally to printed circuit board connectors and specifically to single in-line package (SIP), dual in-line package (DIP), and quad-pack (QUAD) connector systems for use on surface mount technology printed circuit boards.
2. Description of the Prior Art
Forming an electrical connection between separate and different electrical circuits is accomplished through soldering electrically conductive members between the circuits, or by plugging together connectors with each connector half electrically and mechanically attached to the circuits to be connected together.
Electronic circuits have recently become so miniaturized that the connector size relatively dwarfs the circuit it is connected to. In the case of integrated circuit (IC) chips, very small wires are electrically bonded to surfaces of the "lands" on the chip allowing electrical interface with another circuit, usually by means of connection to IC pins and subsequently to other components by being soldered into a printed circuit board (PCB). These IC pins are actually individual projections from a lead-frame, a fabricated metal structure with small details (leads) usually integrally connected to a supporting structure (frame). These are later separated from the frame by various means leaving a group of electrically isolated contact pins. Another method of electrical connection between the chip and lead-frame is surface mount technology (SMT). In SMT, the lead-frame, a continuous metal strip with pins, receives the circuit substrate (chip). Surface-mount components do not mount on a PCB in a "through hole," but rather they are held by solder at a flat, surface solder pad on the PCB. Solderable flat surfaces of the lead-frame are brought into parallel surface contact with the solderable flat surfaces of the chip and then soldered.
Mounting components on the surface of a PCB (e.g., SMT) involves the application of a highly viscous solder alloy by silk-screening methods to various solder joint locations on the flat surface of the PCB. Such a solder "paste" will retain the loaded components in the correct position up through the soldering process. Reflow soldering--where the PCB carrying the loaded components and the solder paste is baked in an elevated temperature chamber--is achieved when the joint temperatures reach about 250.degree. C. Reflow temperatures are commonly accomplished by "vapor phase" or infra-red technologies. Either way, the solder paste liquifies and coats the solder contacts of the respective parts and the PCB's solder pads. Thereafter the cooling of the assembly causes solidification of the solder, and electrical and mechanical bonding of the surface mounted component to the PCB is completed.
Through-hole soldering--in contrast to SMT--requires projections of the components to be inserted into holes drilled through a PCB. Solder is then applied with heat to the projection on the non-component side of the PCB. Wave soldering is a technique commonly employed in high volume production. A consequence of through-hole penetration is equal surface areas on both sides of the PCB equal to the area occupied by a single component are consumed. Through-hole technology therefore reduces the useable PCB area occupied by a single component by one half, compared to SMT.
Both SMT and through-hole soldering technology are conventional, and presently are in wide use in the electronics industry.
Electrical connections made from a PCB to another PCB, or from a PCB to a cable, usually employs electro-mechanical connectors. Socket and PCB stacking interconnect is accomplished in the prior art by discrete screw machine fabricated or progressive die stamped pins, either auto-inserted or manually inserted individually into a PCB or into a plastic connector body. In the latter case, the projecting non-press fit pins are thereafter inserted through holes in the PCB and then soldered to provide both mechanical and electrical integrity. Today, both round and square pins are popular, and both are available in plastic strips that hold the pins at a particular pin to pin spacing (e.g., 0.1"). In response to the increased electronic industry demand for surface mounted connectors, various manufacturers have responded by simply bending the projecting pins laterally outward from the longitudinal center line of connector, at right angles to each, such that the right angle surfaces of the in-line pins can be soldered to the top surface of a PCB; instead of the non-SMT practice of requiring the pins to be inserted through some holes in the PCB.
Individually fabricated pins inserted into removable thermoplastic or metal carriers are available which maintain alignment and spacing for placement on PCB's. But no removable carrier for surface mountable PCB pins manufactured from the same piece of material as the demountable pins is known to be available.
The attachment of chip circuits to metal lead-frames is conventional. Even though flat integrated circuit (IC) pins are widely stamp or photo-chemically etch manufactured for attachment to IC packages, no SMT pin arrays are known to be available--this is odd because SMT parts provide the mechanical integrity of connectors and are fabricated similarly to lead-frame technology. The U.S. Pat. No. 4,054,238 ('238) of Lloyd, et al., is an example of a continuous strip of lead frames that are attached to substrates using through holes. The free ends of lead frame pins have a tendency to be bent and to lose their parallel alignment with one another, thus causing a pin misalignment in the finished assembly.
Ceramic IC packages, with solder lands on the two opposite long sides to receive pins, presented a special case in U.S. Pat. No. 4,232,815 ('815) by Nakano, et al. The solution involved lead frames that are bent into U-channels and have two rows of pins attached at one end on two rows of carriers, called lead frame rail members, which are spaced equal to the width of the ceramic IC. Since the pins in Nakano, et al., are floating at one end, the end by the way that will receive the ceramic IC, there is a chance the introduction of the ceramic IC will cause a few of the pins to be bent out of alignment with one another. The Nakano patent outlines the means of attaching a substrate (ceramic IC) to the lead-frame as a production means.
The U.S. Pat. No. 3,859,718 ('718) of Noe addresses the problem of pin bending on a lead frame by carrying all the pins (for dual in-line applications) at a point across their centers. A "punching means" removes the carriers after the lead frames are soldered to the circuit. Carrying the pins at their centers doesn't prevent the pins from twisting axially about their carriers, and so only the direction of possible pin misalignment has been changed. In addition, a disadvantage of using a punching means is that the PCB must not interfere with the punch's access, and a further disadvantage is the punching means itself is an expensive apparatus that is best eliminated altogether, if possible. A similar lead frame to Noe is found in U.S. Pat. No. 4,439,918 ('918) of Carroll, II, et al. The center strip in Carroll, II, et al., is called a "tie bar" and is said to hold individual pins in alignment and groups of pins together in continuous strips. The tie bars are removed, after soldering and package molding, by a cutting and trimming step. Both Noe and Carroll teach a means to manufacture IC's that attaches substrates to continuous strip lead-frames. Neither teaches single piece lead-frames which are designed to be individually handled and attached to the flats of a substrate.
A pair of attached support carriers is to be found in the U.S. Pat. No. 4,178,678 ('678) of Carillo, et al. Each contact (pin) is carried between a pair of support carriers, but those carriers are severed at a first station, leaving only an adhesive tape to maintain the contacts' alignment. The contacts and adhesive tape are then brought into position with a PCB and then soldered. The adhesive tape is thereafter removed. Carillo, et al., demonstrate only a through-hole PCB application and are silent on how the contact pin alignment is maintained through the removal of, what must be, a very strong adhesive tape. They are similarly silent on the application of the described means with regard to the extremely corrosive surface mounting technology and elevated temperature affects on the performance of adhesive tapes, and the circuit contamination which may result from inadequate tape residue removal.
Two carrier strips are used in the U.S. Pat. No. 4,616,416 ('416) of Cabaud, albeit for all but the most important time which is just before pin soldering. In Cabaud, contact pins are arranged alternately head-to-tail between the two carrier strips. The heads of each contact pin are severed from the respective carrier strip it's attached to, and two half-population strips result, each carrying pins by their tails. The duration of time that the pins with these free ends are exposed to the risk of bending is shortened in Cabaud, but not eliminated. Unfortunately, the greatest risk of inadvertent bending of pins on their carriers will occur as the contacts and their respective carrier strips are being brought into position with the PCB just before soldering.
The difficulties that are encountered in the prior art in attaching various pins and connectors arranged in single in-line and dual in-line configurations on SMT PCB's include: unstable, high center of gravity pins which fall over during the pin installation and SMT reflow soldering process, uncontrollable positioning of precise pin and row spacing and parallelism, temperature expansion coefficient differences between dissimilar materials used for pins and pin carriers, high cost of individual placement or insertion of discrete pins or pin strips, higher cost of drilling individual holes in the PCB for pin mounting, higher costs of bending pins on connectors intended for through-hole insertion to accommodate SMT soldering, yet higher costs of replacing low cost plastics with high temperature plastics resistant to high surface mount soldering temperatures, impracticality or difficulty of removing pin spacing tie-bars from the assembly by special cutting or punching tools, and decreased PCB density resulting from a loss of PCB real estate to the area consumed by otherwise unnecessary through holes. A single, easily removable carrier strip can reduce these and other problems.
Whether one carrier strip or two are employed, the most critical end to maintain in pin to pin alignment is the end that is to be soldered to the PCB. With through-hole PCB's, that end has to, of course, pass through a hole, and therefore couldn't be simultaneously left attached to a carrier strip. In SMT PCB applications, this isn't true, and the soldered end of a contact pin can be left attached to a carrier strip, with the additional benefit of maintaining pin-to-pin alignment throughout soldering. The present invention has therefore become commercially useful since the recent widespread use of SMT PCB's has occurred.
Whenever a carrier strip is to be separated from the contact pins that the strip has served to carry, the removal can be assisted and confined to a proper zone by specially weakening the joints between the contact pins and the carrier strip. Such a feature is to be found in U.S. Pat. No. 3,750,252 by Landman. The carrier strips in Landman are broken away from the terminal legs (contact pins) at weakened areas, such that the terminal legs are thereafter electrically isolated. Alternatively, Landman suggests that the carrier strip may be automatically cut from the terminal legs (ostensibly by a machine). No known prior art, however, discusses ripping a carrier strip off the contact pins one-by-one in a zipper fashion, and none discusses designing a weakened area to facilitate a tearing, rather than a folding action, in removing the carrier strip. The folding action is restricted in SIP applications due to interference from the SMT PCB itself, and impossible in DIP applications were attachment is made at both ends of a folding action's lever. Additionally, no known prior art discusses use of a carrier strip for handling, packaging, robot loading to the PCB, or otherwise being used for a reason other than to maintain relative pin alignment on a strip prior to soldering to a PCB.